A former barrister, Mrs Pengelly was employed as a £92,000-a-year special adviser (Spad) to Mr Robinson and she is widely viewed as a rising star within the party.

Appointments to Stormont committees are the prerogative of the parties, who choose the most suitable candidate for the post.

And, while no one doubts Mrs Pengelly's personal integrity, some will view her appointment as controversial.

Nama's 850-property Northern Ireland portfolio was bought by a US investment firm in April 2014.

It has been alleged in the Dail that £7m in an off-shore bank account linked to the deal had been earmarked for a Northern Ireland politician.

Last week it was claimed that Mr Robinson was one of five people due to benefit from the sale.

Mr Robinson has strongly denied the allegations.

Last night TUV leader Jim Allister said: "I think it's a questionable appointment because of the public perception.

"She is now part of an investigation that reaches into the heart of the office she has just left."

Mrs Pengelly was chosen to replace Jimmy Spratt, the DUP's South Belfast MLA, who stepped down due to health reasons.

Her appointment was announced on Monday.

The appointment of Mrs Pengelly and Mr Lyons to the finance committee emerged in a briefing paper circulated to MLAs yesterday. They will be formally nominated on Monday.

When contacted yesterday, Mrs Pengelly said she had no knowledge of her appointment.

"I am not involved in it at the minute. I understand there is a proposal put forward by the party for the business committee, so I wouldn't be in a position to confirm that," she said,

"I am not clear about what committee I am going on to."

Mrs Pengelly's husband, Richard Pengelly, is the permanent secretary of the Department of Health and was one of three people nominated to sit on Nama's Northern Ireland advisory committee, although he didn't end up in the role.

It was set up in 2010 as a compromise after then Irish Finance Minister Brian Lenihan ruled out a Northern Ireland presence on the Nama board. Party sources said Mr and Mrs Pengelly were not in a relationship at the time.